<?php
$url = "index.html";
$file = file_get_contents($url);
$doc = new DOMDocument();
$doc->encoding = "UTF-8";
$res = $doc->loadHTML($file);
$items = $doc->getElementsByTagName('input');
$cnt = $items->length;
$str = $items->item(0)->getAttribute('value')."\n";
$str = mb_convert_encoding($str, "UTF-8", "auto");
echo $str;
?>

サーバ側もindex.htmlもencodingもUTF-8にしたのに文字化けしてしまいます